The principle goal of this project is to identify the cellular states and signals that control cell types and synapses in the central nervous system. The identification of stem cells in the central nervous system has led to the realization that large numbers of stem cells are present during brain development and that they share many differentiation mechanisms with stem cells present in the adult brain. In the past year we have: (1) reported on the analysis of a new protein that is specifically expressed in stem cells and is of great interest because it binds the tumor suppressor p53 and regulates the cell cycle; (2) described a new signaling mechanism that controls the action of the extracellular factor, BMP on stem cell fate choice; (3) shown that neurons can survive in vivo in the absence of the major glutamate receptor (NMDAR1). In these studies we continue to define the basic molecular mechanisms controlling the number, type and function of cells in the nervous system.